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May 18, 2011 -- Most women aged 30 and older with normal Pap and human paillomavirus (HPV) test results can safely wait three years until their next set of cervical cancer screening tests, according to a new study.

Such co-testing is currently recommended by the American Congress of Obstetricians and Gynecologists. The guidelines note that women with certain risk factors for cervical cancer may need more frequent testing.

The new study, which will be presented at a meeting of the American Society of Clinical Oncology (ASCO) in Chicago, should ease doubts about the safety of these recommendations.

The findings also hint that HPV testing alone may be more accurate than Pap testing alone in predicting future cervical cancer. "The Pap testing screening program has greatly reduced rates of cervical cancer, but 11,000 women are still diagnosed every year and 4,000 women die from cervical cancer each year," said Hormuzd A. Katki, PhD, in a news conference. Katki works in the division of cancer epidemiology and genetics at the National Cancer Institute in Bethesda.

HPV causes most cases of cervical cancer, and incorporating HPV testing into cervical cancer screening programs can catch more at-risk women. During a pap test, a doctor scrapes cells from a woman's cervix and a laboratory examines these cells for abnormalities. When a type of Pap test called a liquid-based cytology test is performed, testing for HPV can be performed at the same time.

In the new study, researchers categorized 331,818 women aged 30 and older based on the results of their HPV and Pap tests, and estimated their risk of developing cervical precancer or cancer during the next five years. These women were enrolled in Kaiser Permanente Northern California's co-testing program between 2003 and 2005.

Cervical Cancer Risk

The five-year risk of cervical cancer seen among women with both normal Pap and HPV results was 3.2 cases of cervical cancers per 100,000 women per year.

When looking at HPV and Pap testing separately, women who tested negative for HPV had a five-year risk of 3.8 cases of cervical cancer per 100,000 women per year. Those with a normal Pap test result had a five-year risk of 7.5 per 100,000 women per year.

"HPV testing is better able to separate women into high risk of cervical cancer and low risk of cervical cancer than the Pap test," Katki says. But "this does not mean that Pap test is useless."

If confirmed by future research, "instead of co-testing in which women get both tests at every visit, they can get HPV tested first and HPV-negative women would be asked to return in three years," Katki says.

Pap testing would be based on HPV status, he says. "This would reduce Pap tests by 95% -- and retains all of the safety of co-testing."

"This news is very reassuring" says ASCO President George W. Sledge, the Ballvé-Lantero Professor of Oncology and professor of pathology and laboratory medicine at Indiana University School of Medicine in Indianapolis. "The uptake of the co-testing recommendations has not been perfect within the cervical cancer community due to concerns about risks of waiting that long between tests."

"This gives us great reassurance that we can test every three years safely and that it is absolutely possible to remember to keep coming in every three years," he says.